You would think calcium supplementation would be a simple subject, but it is not. Lately, studies have been quite mixed in terms of the benefits and risks of taking calcium supplements.
What we can agree on is that calcium is not something that anyone wants to be deficient in. Deficiency in calcium and/or vitamin D (which increases calcium absorption) has been correlated to bone loss, hypertension, and cancers of the colon and breast:
Higher calcium intake may be protective against developing kidney stones:
When calcium intake drops, parathyroid hormone increases, which causes calcium to be pulled out of the bones for use elsewhere (such as to buffer the blood). High parathyroid hormone levels (which typically result from low calcium intake) have a negative impact on health, as discussed by Ray Peat, PhD, in this article:
In recent years, there is conflicting evidence as to whether calcium supplements may increase cardiovascular risk. Epidemiological studies (which are more definitive than meta-analyses) however have not reflected a risk:
In looking at some of the largest studies on calcium intake and disease risk, my conclusion would be that calcium from dietary sources does not appear to be correlated to risk, but when calcium supplements are involved, there may be an increased risk (of myocardial infarction or heart attack):
This would strongly suggest that the source of the calcium is what makes all the difference. We should all try to get calcium primarily from our diet. However, if you're going to supplement calcium, I believe it makes sense to only take calcium from a product that is plant or food based. Some examples of plant/food calcium include high quality coral-based calcium, egg-shell calcium, and algae-based calcium. Another benefit to food-based calcium is that it appears you don't need to take as much due to increased bio-availability.